Conventionally, various considerations have been made to decrease cutting resistance in a cutting tool that uses cutting inserts by attaching them to insert pockets of a holder. For example, as in the case of Japanese Unexamined Patent Publication No. 2008-544872, the cutting resistance is decreased by inclining a ridge line of a major cutting edge of the cutting insert to make adjustments so that an axial rake angle of a major cutting edge has a positive angle, or by increasing a peripheral cutting edge angle of the major cutting edge.
However, for example, when the peripheral cutting edge of the major cutting edge is increased, the cutting resistance is decreased because chip thickness is decreased, whereas a component force (thrust force) of a cutting force oriented rearward of a rotation axis is increased. Additionally, in this case, when two constraining faces that constrain the cutting insert are formed substantially line-symmetrically at a predetermined angle with reference to the rotation axis direction in the insert pocket, as disclosed in Japanese Unexamined Patent Publication No. 2008-544872, the following problem might occur.
That is, the cutting tool receives such action that a gap between the two constraining faces of the insert pocket is expanded by the thrust force described above. Therefore, by repetitive cutting using this cutting tool, the constraining faces of the insert pocket of the holder are subjected to plastic deformation, so that the fixation of the cutting insert may become unstable.